I once attended a lecture by a philosopher who, in the midst of a tirade against the Christian right, interrupted himself and admitted that his atheism also had a problem: “I hate to admit it,” he conceded, “but I am a qualia freak.” Among philosophers working on the mind/body problem, the word “qualia” stands for all those features of consciousness that give awareness its specific identity as a particular kind of experience: the redness of red, the sadness of depression, the piquancy of papaya juice, the irksomeness of traffic jams, the crankiness that comes from insomnia, the hurt feelings arising from playground taunts, and so forth.

Here’s the problem in a nutshell: there seems to be no immediately obvious scientific explanation for how electrical firings inside the brain can give rise to these peculiar qualia. What does electricity, shooting through the raw meat of the brain, have to do with supply-side economics, office politics, or misunderstandings in a marriage?

Qualia constitute the central challenge for any philosopher who wants to provide a fully naturalistic account of consciousness based on the neurochemistry of the brain. Does consciousness add something to the workings of the brain, with it controlling them (at least in some circumstances, like the decision to pick up a pencil)? Or is it merely the product of brain events, with no more role in running the operations of the cerebellum than steam has in causing heat in a teakettle? If computers can crunch numbers better than humans, and if they can beat chess masters at their own game, all the while being totally unconscious and just blindly following an algorithmic computer program, can they also someday mimic all human behaviors without exception, while also still remaining utterly unconscious? (Noam Chomsky, for one, says that to call a chess-playing computer “intelligent” is like entering a forklift in an Olympic weight-lifting competition and giving it the gold medal for its greater hefting prowess.)

Of course, the question works both ways. If a finely-tuned robot could mimic all human behaviors (including reporting what would be pain if it were human), then the mechanical naturalists would have proved their point that the brain is nothing more than computerized flesh”or so they claim. But others, like philosophers John Searle and Thomas Nagel, say that even if such a robot could be invented, it would be, by definition, a “zombie” (another overworked term in the mind/body lexicon). In other words, such a robot would merely be a more extreme version of a human sleepwalker, an automaton that does things by program and not by conscious decision. But everyone knows, simply by consulting his own experience, that the alleged “program” of the human brain results in something more than a sleepwalking ability to avoid bumping into things and to get snacks out of the refrigerator unawares.

Dennett calls this common objection to his project the “Zombie Hunch,” meaning the queasy sense most of us have that materialists like Dennett have left something out. (One reviewer of Dennett’s earlier book Consciousness Explained said the title should have been Consciousness Explained Away .) He counters this hunch by extending it, in a strange thought-experiment, to Martian zombies sent to earth as anthropologists to study human behavior. By hypothesis they cannot get inside the human minds of their subjects, since they have no intersubjective substrate of their own. According to Dennett, these Martian anthropologists would then discover that human behavior in fact displays no such intersubjectivity of its own either: Everything the Martians see in the way humans act can be explained by the standard norms of their science, and since they are missing that extra mental stuff, why assume humans have it either?

As should be immediately obvious, such an interplanetary project requires the personal motivation of extraterrestrial ambition, research grants from the Martian Institute of Technology, heated argument among the little green men, and so on”which means Dennett has already introduced mental awareness into his thought-experiment, a point that will strike the reader when the author describes the behavior of his exo-anthropologists:

For the sake of argument consider that the Martians might be zombies, whose data-gathering and scientific theorizing [are] all accomplished without a trace of “phenomenonality” or “qualia” or whatever you take to be the hallmark of real consciousness . . . . [These] Martians would soon discover that a scientific theory of consciousness is widely held by Earthlings to be impossible . . . . And more importantly, what would they make of the hypothesis that there was something that they, the Martians, couldn’t know about human consciousness that we, the Earthlings, can know? . . . One of the texts that the Martians would surely study is Descartes’s Meditations (1641) and they would find it speaking forthrightly to them.

With such phrases as “would soon discover,” “what would they make,” and “they would find,” Dennett is forced to slip in non-Zombie verbs to make his thesis work. (One savors the irony that these lines come from the same man who insisted in an op-ed article for the New York Times two years ago that society should start calling atheists “the Brights” because they’re so much smarter than theists. Right.) An even more bizarre passage occurs a few chapters later: “One of the themes about qualia that is often presupposed but seldom carefully discussed was memorably made explicit for me by Wilfred Sellars, over a fine bottle of Chambertin, in Cincinnati in 1971: I had expressed to him my continuing skepticism about the utility of the concept of qualia and he replied: ‘But Dan, qualia are what make life worth living!’”

Indeed. They are also what can make life hellish, aggravating, or anxiety-ridden”not to mention what allow us to call a bottle of Chambertin “fine.” In other words, experience is inherently an experience of qualia (just try to imagine an experience without them). In fact, so much are qualia the inherent objective pole of all experience, reading Dennett’s book suddenly made me realize what Bishop George Berkeley was driving at when he called his philosophy of subjective idealism a republication of common sense. He is famous (or notorious, if you prefer) in the history of philosophy for his principle esse est percipi (to be is to be perceived), which was popularly taken to mean that if you’re not aware of something, it doesn’t exist, a conclusion the bishop himself was able to avoid by relying on God, the All-Perceiver, to keep things in existence while we’re nodding off during atheists’ lectures, a divine escape-hatch wittily satirized by the famous limericks often ascribed to Ronald Knox:

There was a young man who said “God Must think it exceedingly odd If he finds that this tree Continues to be When there’s no one about in the Quad.”

“Dear Sir, your astonishment’s odd; I am always about in the Quad And that’s why this tree Will continue to be Since observed by . . . Yours faithfully, God.”

So who is reviewing this book? A collection of robotic cells that is churning out a review claiming to disagree with the book because the organism cranking it out happened to go through a peculiar form of religious upbringing that led him to become a Catholic priest? Or is he a solipsistic Berkeleyian ego who has been so bombarded with sense impressions and qualia his whole life that he can’t find convincing any attempt to explain away consciousness by means of neurology?

In his Apologia Cardinal Newman said that as an adolescent he could acknowledge only two realities, God and his soul, to such an extent that it was difficult for him to believe in the reality of the material world. As Dennett’s title openly asserts, materialist accounts of consciousness continually run into snags”and reading his attempt to answer those objections had the paradoxical effect of making me see Newman’s point. So I turned to the writings of the English cardinal himself and found an infallible sign of his genius: Well over a century and a half before Dennett sat down at his computer to write his book, Newman had already reviewed it. In The Tamworth Reading Room (1841) he wrote:

Physical philosophers are ever inquiring whence things are, not why; referring them to nature, not to mind; and thus they tend to make a system a substitute for God . . . . The study of Nature, when religious feeling is away, leads the mind, rightly or wrongly, to acquiesce in the atheistic theory, as the simplest and easiest. It is but parallel to that tendency in anatomical studies, which no one will deny, to solve all the phenomena of the human frame into material elements and powers, and to dispense with the soul. To those who are conscious of matter, but not conscious of mind, it seems more rational to refer all things to one origin, such as they know, than to assume the existence of a second origin, such as they know not . . . . If we come to [nature] with the assumption that it is a creation, we shall study it with awe; if assuming it to be a system, with mere curiosity.

This can hardly have been his intention, but Dennett’s exuberant curiosity, vivid writing style, and, above all, his forthright attempts to deal with the enigma of consciousness in terms consonant with his mechanical naturalism, will have the paradoxical effect of bringing his readers to a renewed sense of awe at the miracle of the soul.

Edward T. Oakes, S.J. teaches theology at the University of St. Mary of the Lake, seminary for the archdiocese of Chicago